Gas turbine engine blades used in the engine's turbine section are typically cooled via internal cooling channels through which compressed air is forced. This compressed air is typically drawn from a supply of compressed air created by the engine's compressor. However, drawing of the compressed air for cooling reduces the amount of compressed air available for combustion. This, in turn, lowers engine efficiency. Consequently, minimizing the amount of cooling air withdrawn from the compressor for cooling is an important technology in modern gas turbine design.
In some gas turbine engine models downstream blades extend relatively far in the radial direction. Downstream blades may include, for example, a last row of blades. Cooling channels typically direct cooling air from a base of the blade toward a tip, where it is exhausted into a flow of combustion gases. By virtue of the cooling channel extending within the blade so far radially outward, rotation of the blade, and the cooling channel disposed therein, imparts a centrifugal force on the cooling air that urges the cooling air in the cooling channel radially outward. The cooling air exits the blade and this creates a flow of cooling air within the cooling channel. This flow within the cooling channel creates a suction that draws more cooling air from a rotor cavity around the base of the blade into the cooling channel. Consequently, unlike convention cooling where compressed air is forced through the cooling channels, air that is not compressed, such as ambient air present outside of the gas turbine engine, can be used to cool the downstream blades.
A static pressure of ambient air is sufficiently greater than a static pressure in the rotor cavity to produce a flow of cooling fluid from a source of ambient air toward the rotor cavity. Thus, a static pressure of ambient air may push a supply of ambient air toward the rotor cavity, where a suction generated by the rotation of the blades then draws the ambient air from the rotor cavity through the cooling channels in the turbine blades, thereby completing an ambient air cooling circuit. The suction force aids in drawing ambient air into the rotor cavity. In this manner a flow of ambient air throughout the cooling circuit can be maintained.
However, a static pressure of ambient air within the rotor cavity is not substantially greater than a static pressure of combustion gases in a radially inward region of the hot gas path. The static pressure of the combustion gases in a radially inward region of the hot gas path may vary circumferentially and there may be transient operating conditions that produce static pressure differences in the combustion gases. These conditions may lead to ingestion of hot gases through a rim seal separating the rotor cavity from the hot gases in the radially inward region of the hot gas path. Ingestion of hot gases may be detrimental to a life of the engine components. Thus, there is room for improvement in the art.